Roulette Croupier Manipulation?

[oscark]

I was in a discussion with several casino employees. They claim many practiced Croupiers, using the right timing and force, can make the ball lands in a certain sector of the wheel at a much higher frequency than standard, making it profitable (and illegal) for him or her to team up with someone on the outside.

Is this possible? How do Casinos protect against it?

Thanks,

Oscar